Thursday, April 30, 2009

One can hardly improve upon the many posts and articles regarding the N-Prize, which has now been active for quite some time. We have discussed many of the possible plans and debated everything including the value of such a competition; one that is nearly impossible to complete. But all the same, there have been no substantial posts on this subject here at High Power. Below are some most relevant links, divided into general information and teams. This post will also be placed, along with any future rocketry posts not directly related to the N Prize, at the usual High Power Rocketry Page; High Power Rocketry.

The official rules are:

"The challenge posed by the N-Prize is to launch a satellite weighing between 9.99 and 19.99 grams into Earth orbit, and to track it for a minimum of nine orbits. Most importantly, though, the launch budget must be within £999.99 (about $1500) - and must include the launch vehicle, all of the required non-reuseable launch equipment hardware, and propellant."

The reward is about $15,000, but really the reward is doing something very very hard.

I would like to finish this brief discussion with my, purely hypothetical proposal to achieve the prize. Many of the above listed teams have great plans, some are traditional and others quite unconventional to say the least.

My plan:

The launch team would prepare a large helium balloon, probably an inexpensive homemade zero pressure balloon suitable for flight to or slightly above 100,000 feet altitude (near space.) -*Update, I have since noticed just how expensive helium is. Either the team may have to brew their own hydrogen, or perhaps use a solar balloon which uses plain air and can only fly to lower altitudes, but at greatly reduced prices. These solar balloons can actually be built very large for a low cost, perhaps allowing for more lift.*- Indeed if possible, 110,000 feet or 115,000 feet would greatly increase performance at little additional balloon costs. Attached to this balloon, large enough to carry approximately 100 lbs. to near space, will be a gondola package, launch tower, and rocket system. The electronics and documentation package will be maximally lightweight, on the order of 1 kg. The launch tower will also be as light as possible, made of carbon fiber or other composites (more on how to avoid the high cost of this item below), and will likely be on the order of 10 feet long. Most importantly, the rocket system will consist of an amateur O motor contained within a very light weight, minimum diameter dart airframe. This should be a high thrust O motor, an O 10,000 would be a suitable choice, or perhaps faster still. The reason for this is to achieve aerodynamic stability quickly in the thin air, which will be assisted by a 5 - 8 rps spin:

The rocket is to be fired at a 45 degree angle. At burnout, this rocket is expected to achieve a velocity of at least 5000 fps. This is, however, far short of what is required for orbit. After a short coast period, sufficient to allow the rocket to achieve an altitude of more than 50 miles, the second and final stage of the launch process will be ignited. However, as a result of the high cost of conventional rocket stages (rapidly pushing the price point over the limit), this 2nd (or perhaps 3rd) stage will consist of a shaped charge:

A powerful conic shaped charge will ignite. At the focus of this shaped charge, there will be a small metallic slug. This slug is to be lunched into orbit. This metal slug will consist of several layers, and will retain a basic useful form as in explosively shaped projectiles (see below.) Within the metal projectile, a burning thermite charge could eject chaff into orbit (for the sake of government assisted tracking), or some gas could be evolved from a filler material that will glow against the night sky and be visible from ground based telescopes. This may be compared to a tracer bullet, though it would have a full thickness of tracking material, sufficient to remain visible for 9 orbits:

This project minimizes to (according to my understanding) the lowest possible disposable cost, given a reasonable and realistic initial investment. The per launch cost, per the prize rules, would consist of the rocket propellant, shaped charge, balloon, and helium (or hydrogen). It is expected that the rocket proper and gondola and tower structure will be recovered. Having said that, it is hard to see how a small rocket launched at a 45 degree angle, into space or near space, could ever be recovered. This flaw may still not break the budget as a complete O motor and rocket could probably be built for a reasonably low cost, less than half of the total budget.

Finally, it should be noted that shaped charges seldom launch solid objects at hypersonic velocity, but in this project, nothing short of 15,000 fps is needed. This would likely be a record, and requires some really smart shaped charge design (if it is possible at all.) It may be that a 2nd or even 3rd stage would be needed to assure orbit. Also, care must be taken to avoid too much velocity, which could cause solar orbit. Perhaps using several stages could allow orbit without a shaped charge, but at what cost and complexity increases? I would welcome any comments about this plan.

This type of small object in orbit, while hardly as useful as a pico-satellite, could still allow for some limited science. The rate of decay of orbit could help refine atmospheric density measurements (as if we need more of that by now). Also, and probably most important, the tiny metal slug would allow for practice tracking very small objects. Perhaps it can help us simulate what happens to space junk after collisions and explosions in LEO, something that sadly may become more common.

Future posts may explore more about individual teams and their attempts.